There are a variety of ways known for securing a printing plate to the outer surface of a printing plate roller used in a rotary printing press, such as a flexographic printing press. In flexographic printing, for example, the printing plate is flexible, can be easily conformed around the printing plate roller and typically includes a plastic film, such as mylar, mounting a layer of elastomeric material, with an embossed area forming the image to be printed. Such printing plates are often sensitive or structurally weak (i.e., the printing surface is susceptible to damage). One way used to secure such a printing plate is to mount the plate to a backing made of a structurally strong material (e.g., brass) which is formed to fit around but not completely around the plate roller, leaving two ends of the backing with a gap between them. Some form of clamping mechanism is used to secure the backing of the printing plate around the plate roller. The clamps are typically not directly securable to the printing plate without causing damage to the plate. Adhesive systems have also been used to attach the printing plate to the plate roller. Such adhesive systems have included the use of double-sided adhesive tape and spray-on adhesives which have been applied between the outer surface of the plate roller and the back of the printing plate.
Securing the printing plate with clamps requires the use of the backing, which increases costs. In addition, the plate is usually permanently mounted to the backing which limits the possible orientations of the printing plate on the plate roller. Using an adhesive, on the other hand, enables the printing plate to be attached directly to the plate roller without the backing and in a broad range of orientations. However, the use of an adhesive has its own drawbacks. Removal of such an adhered plate may cause the plate to deform, tear or otherwise become damaged, especially if it is a sensitive printing plate. Inconsistencies in the adhesive thickness and the compressibility of the adhesive layer can cause quality problems with the printing process. In addition, removal of the adhesive from the plate roller and printing plate often requires a time consuming and costly cleaning step to remove any adhesive residue.
Another way to secure a printing plate to a printing plate roller is to form a vacuum between the outer surface of the roller and the back of the plate. By using a vacuum to secure the printing plate to the plate roller, the above problems can be avoided. There are a number of prior printing plate roller designs which use a vacuum to secure the printing plate to the roller. However, even with their drawbacks, various clamping and adhesive systems are still being used. It is believed that one reason for the continued use of clamping and adhesive systems is that prior vacuum systems (i.e., the printing plate roller designs) are relatively complex and costly to manufacture.
Therefore, there is a need for a printing plate roller which utilizes a vacuum to secure a printing plate to its outer surface which is relatively simple in construction and inexpensive to manufacture.